Engines may use a turbocharger to improve engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side and the compressor is coupled to an intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. Monitoring the air mass flow rate into the engine may help determine fuel injection amount for example, or may assist in controlling exhaust gas recirculation.
One example to address monitoring air mass flow rate is to use mass air flow sensors such as a hot wire sensor, wherein the change of resistance of the wire responsive to temperature is calibrated into an air mass flow rate by a controller.
However, the inventors have recognized potential issues with such systems. Mass air flow sensors such as hot wire sensors may form deposits from contaminants, especially when operating in urban areas, thereby decreasing in measurement accuracy over operational time.
One potential approach to at least partially address some of the above issues includes a method for determining a charge air mass flow rate, herein also air mass flow rate. The method comprises determining an open loop air mass flow rate from a characteristic field stored in an engine controller, wherein the open loop rate is a function of a measured pressure compressor ratio and measured turbocharger revolution rate, i.e. turbine speed. The method further comprises modeling an associated turbocharger revolution rate and determining a closed loop air mass flow rate, wherein the closed loop air mass flow rate is the sum of the open loop rate and an offset value.
In one example, closed loop air mass flow rate is determined repeatedly, wherein each case the previously obtained closed loop air mass flow rate is used to model the turbocharger revolution rate. In turn, a controller may adjust other engine parameters, such as fuel injection time, fuel mass balance, and air-fuel ratio, based on the updated charge air mass flow rate. In this way, each measurement of the charge air mass flow rate is updated and corrected upon successive cycles, producing more accurate measurements than those determined solely on open loop values, for example. Further, this method of determining charge air mass flow rate may be done without a mass air flow sensor for example, and therefore measurements do not depend on conditions that may degrade sensors upon deposition.
In another example, a method comprises adjusting an engine actuator responsive to an air mass flow rate, the air mass flow rate not based on a mass airflow sensor and based on an error between an estimated turbine speed and a measured turbine speed, the estimated turbine speed based on a load balance on a turbocharger shaft.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.